Most existing RF transmitting devices perform a so-called direct frequency conversion from baseband to RF of the signals to transmit. Such a frequency conversion can be classically carried out by means of a single-sideband IQ RF mixer (in which input data used to modulate a carrier are decomposed (or split up) into in-phase (I) and quadrature (Q) data) or a polar device (in which input data used to modulate a carrier are decomposed (or split up) into phase data and amplitude data). Examples of digital polar RF transmitting devices are notably described in the patent documents US 2005/0116786, US 2005/011685, US 2005/0089117 and US 2005/0083085.
As it is known by the man skilled in the art, in both cases in order, the RF transmitting device must be capable of delivering an output signal with a variable radiofrequency, it has to comprise a RF voltage controlled oscillator (VCO) loop locked onto a reference signal having a low frequency, typically in the 10-40 MHz range and generally provided by a quartz oscillator, by means of a RF phase locked loop (or PLL).
Due to the presence of a phase locked loop, the known RF transmitting devices present several drawbacks. First of all, they have difficulties to cover a large frequency range, related to the difficulty to design a wide-band RF VCO. Moreover, they comprise a VCO which is a sensitive module and therefore is susceptible to be disturbed by the transmit RF signal itself and/or by other internal or external RF signals and/or by low frequency signals present on-chip. More, they comprise a phase locked loop which necessitates i) a loop filter that is difficult or expensive to integrate on a chip, and ii) two oscillators (a reference oscillator and a VCO). Still more, when their reference oscillator is a quartz oscillator, they cannot be fully integrated into the package of the transceiver integrated circuit (IC), because of the bulkiness of this type of oscillator.